same problem, somewhat simpler solution
Hello,
I have been having the same problem where I can log into the forums, but it won't recognize when I have logged into the workout manager.
What I did was go the forums, log out, log back in, click on workout manager tab at the top, and when the work out manager page loads, I'm logged in.
I use Firefox too. It is a wonderful browser, very stable. I'm glad they are working to make the Cathe online stuff compatible with Firefox, but we shouldn't have to keep clearing cache, cookies or other stuff to make something work. There is a bug that needs fixing.